CUENCA, Ecuador - Ecuadoran officials are pressing forward Monday with the trial of a Massachusetts fugitive accused of a double murder in Brockton, even as Plymouth District Attorney Timothy J. Cruz continues to fight for his extradition to the United States.

The trial comes nearly a year after a Plymouth County grand jury indicted Luis Guaman on two counts of first-degree murder in the savage beating deaths of his housemates, Maria Avelina Palaguachi and her 2-year-old son, Brian, in February 2011. In Ecuador, Guaman has pleaded not guilty.

The trial, entering its second and possibly final day Monday, has set off a diplomatic clash. Cruz is calling for sanctions against Ecuador for refusing to extradite Guaman to the United States, saying the trial in Ecuador will be “a complete sham.’’

Ecuadoran prosecutors, meanwhile, say Cruz should give up on extradition and help them, as prosecutors in other US cities have done in Mexico. Ecuador’s constitution forbids extraditing its citizens.

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Cruz has refused to cooperate with the prosecution, citing Ecuador’s much lower penalties: a maximum of 25 years for homicide, according to Ecuadoran prosecutors, compared with life in prison in Massachusetts. He also raised concerns about police corruption and the quick trial with none of the physical evidence from Brockton.

“Why would I be a party to this charade? That’s what this is,’’ Cruz said late last week in Massachusetts. “It’s an absolute charade that provides no protection to the people in my county and my state and my country.’’

But Ecuadoran prosecutor Rocio Polo said her case against Guaman is even stronger than the one prosecutors in Florida successfully made in 2006 against Nelson Serrano, a dual citizen of the United States and Ecuador, for four homicides based largely on circumstantial evidence. The Florida Supreme Court upheld the death penalty for Serrano last year.

Polo said she will ask the Third Criminal Tribunal of Azuay, housed in a soaring brick courthouse in the center of this cosmopolitan city, to consider a variety of evidence that includes autopsies Ecuador conducted when the bodies were sent here for burial, Guaman’s decision to leave the United States with another man’s passport, and affidavits from Cruz and others outlining the physical evidence against Guaman, including information that Guaman’s fingerprints were found on the bags in which the bodies were dumped. She is also calling witnesses to testify about his access to the victims. “I have 10 times what they had in the Serrano case,’’ Polo said.

Judicial police in Cuenca arrested Guaman in February 2011 days after he arrived in Ecuador. His estranged wife in New York and others had reported him to police, saying he had called his wife and threatened to kill their four children and her parents if she did not send him money.

Guaman, a 41-year-old roofer who was in the United States illegally, used the passport of another man, who bore only a passing resemblance to him, to get through security at John F. Kennedy International Airport in New York and then fly to Ecuador. He left hours after the bludgeoned bodies of Palaguachi and her son were found in a trash bin behind their house in Brockton.

After the arrest, Ecuador prosecuted Guaman for passport fraud. He was convicted, served time for that charge, and has remained in jail pending investigation of the alleged homicides.

Guaman’s defense lawyer, Italo Palacios, said Guaman had nothing to do with the crimes and left using a passport that wasn’t his because he had problems in New York. Guaman has an outstanding arrest warrant in New York for allegedly kidnapping and assaulting his estranged wife.

On Sunday, Polo said she wished Plymouth County had aided in the prosecution of Guaman, to make her case even stronger. She pointed out that other states and nations have collaborated to prosecute accused criminals.

But officials in California, Texas, and elsewhere, including Los Angeles County Sheriff Lee Baca, have said they are open to prosecutions in Mexico, for example, when extradition is not possible.

The El Paso District Attorney’s office has worked with Mexico to prosecute more than a dozen fugitives, including accused murderers, said Roberto Ramos, head of the DA’s foreign prosecutions unit, created around 2005 in the border city. He said most cases have ended in convictions.

Ramos said El Paso turned to foreign prosecutions when extradition talks deadlocked, usually over Mexico’s opposition in the past to the death penalty.

Ramos said he had not helped prosecute crime in Ecuador and did not have an opinion on the Guaman case. He said Mexican police are often accused of corruption as well, but he said prosecutors in Mexico have allowed El Paso prosecutors to observe the prosecutions.

As Cruz has pushed for extradition to Massachusetts, he has pointed to the state constitutional mandates that crimes be tried where they happened. He said Ecuador initially signaled that it would send back Guaman, then backtracked, citing the ban in its 2008 constitution, which has undergone multiple changes over the years.

Cruz, who has the support of Senator Scott Brown and others, has called for economic sanctions and the halting of trade preferences for Ecuador because he said it is violating its much older extradition treaty with the United States. He pointed out that even if Guaman is convicted, he could serve much less time than the maximum penalty in Ecuador.

The United States is Ecuador’s largest trading partner, according to the US Department of State, and the countries have long enjoyed close ties. Ecuador, a small country of 14 million people, uses the US dollar as its official currency and thousands of American tourists visit Ecuador annually. But the nations clashed in the past year over the Guaman case and other matters. Ecuador expelled US ambassador Heather Hodges last year after WikiLeaks revealed a confidential 2009 cable in which she discussed alleged corruption in the national police force. The United States then expelled Ecuador’s ambassador.

Relatives of Palaguachi and her son have strongly supported Cruz’s efforts to extradite Guaman because he would face tougher penalties in Massachusetts, if convicted. But on Monday two relatives - Brian’s father and one of Palaguachi’s sisters - will testify via videoconference to aid the prosecution in Ecuador.

Manuel Jesus Caguana, who was out of town working when Palaguachi and his son were killed, apparently with sledgehammer blows to their heads, said he decided to testify via videoconference in hopes that Guaman will stay in jail, even if it is on another continent.

“They keep saying no matter what we’re going to bring him back,’’ he said softly, referring to Plymouth County’s efforts to extradite Guaman. “But they haven’t done it.’’

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